Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
325 AM EDT Sun Apr 30 2023

Valid 12Z Sun Apr 30 2023 - 12Z Tue May 02 2023

...Heavy rainfall and severe thunderstorms likely across Northeast and
Mid-Atlantic on Sunday...

...Locally significant, multi-day snowfall event for U.P. of Michigan
through early work week; Well-below-average temperatures across Great
Lakes and Ohio Valley Sunday through Tuesday...

...Above-average temperatures to continue across interior Pacific
Northwest, Great Basin, and Intermountain West, as cooler weather arrives
on Sunday for immediate coast...


The main weather headline for the last day of April will be the heavy
rainfall potential throughout the Mid-Atlantic and Northeast as a
strengthening storm system tracks along the Eastern Seaboard. Sunday will
be a wet and chilly day for the entirety of the region, as the surface low
tracks just inland, allowing for anomalously moist air originating from as
far south as Florida to push onshore, increasing the chances for heavy
rainfall and producing region-wide rainfall totals of 1"+. The heaviest
totals will be confined to coastal and interior northern New England,
where upwards of 3-5" of rain, in addition to rainfall rates approaching
1"/hr will be possible, resulting in the issuance of a Slight Risk of
Excessive Rainfall for northern Massachusetts, New Hampshire, and southern
Maine. Further south, a second Slight Risk is in effect for New Jersey,
eastern Pennsylvania, and southern New York, as although rainfall totals
will not be as excessive as in previously mentioned areas, the combination
of 1-2" of rain and saturated soils, given the recent rainfall, may lead
to areas of flooding as showers and thunderstorms develop on Sunday.
Severe thunderstorms will also be of concern across the Carolinas and
Mid-Atlantic ahead of the frontal passage during the early to midday
Sunday hours, with damaging winds and isolated tornadoes possible,
resulting in the Storm Prediction Center placing much of the region under
a Slight Risk for Severe Thunderstorms. Conditions will improve from south
to north, with the heaviest axis of precipitation pushing through northern
New England during the early Monday morning hours, although the weather
will remain damp and cool through Tuesday.

Meanwhile, a deepening, highly anomalous, and nearly stationary upper-low
presiding over the Great Lakes will lead to much below-average
temperatures and localized heavy snowfall across northern Wisconsin and
the Upper Peninsula (U.P.) of Michigan through Monday. Shortwave energy
traveling around the base of the upper low will lead to a rapid deepening
of a surface low over Lake Superior and the Ontario Province late Sunday
into Monday, with several locations potentially approaching both April and
May monthly low-pressure records. Strong northwesterly winds on the
backside of the strengthening surface low, in conjunction with cold air
advecting southward and orographic lifting, will lead to a localized swath
of 1-2ft of snow across higher elevations of the interior U.P. of
Michigan. Given the late-season snow, surface temperatures hovering around
freezing during the event will lead to very heavy wet snow, which may
result in downed trees and powerlines. The snow will diminish on Tuesday
as the system weakens and slowly pushes eastward as high pressure builds
in. Furthermore, a broader area of much-below-average temperatures (10-20
degrees F below average), encompassing much of the Midwest, Great Lakes
region, and Ohio Valley, will be possible through Tuesday, as daytime
highs struggle to reach 50F, and numerous locations approach or break
daily record low maximum temperatures.

Elsewhere, above-average temperatures across the Intermountain West, Great
Basin, and interior Pacific Northwest will continue through the forecast
timeframe as persistent upper-level ridging supports temperatures 15-25
degrees above normal. Widespread high temperatures in the 80s are expected
throughout interior sections of the Pacific Northwest, while locations
further south, including California's Central Valley and the
Mojave/Sonoran deserts, reach the 90s and even 100s in localized areas on
Sunday. However, a storm system and attendant cold front pushing onshore
early Sunday will result in more seasonable temperatures returning to the
immediate coast, with cooler temperatures spreading inland on Monday and
Tuesday. Furthermore, scattered showers, thunderstorms, and high-elevation
snow will also be possible across the West and northern/central Rockies
during the start of the work week.


Russell


Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php